The present invention relates to an electronically controlled microwave dielectric panel lens having improved bandwidth and reduced biasing requirements.
As illustrated by U.S. Pat. No. 3,708,796 issued to M. Gilbert Bony electronic scanning lens are known which are made up of one or more dielectric panels positioned one behind the other in parallel planes perpendicular to the direction of propagation of an incident electromagnetic microwave. Each panel of such lens is constructed of dielectric material in which are mounted a plurality of conductors or leads such as metal wires. Preferably the incident microwave has a fixed linear polarization and metal wires are embedded in the dielectric panels parallel to the electronic field component of the linear polarized incident microwave.
In accordance with the teachings of Bony, a plurality of diodes are spaced apart on each wire in series combination. The diodes of each wire are all aligned in the same direction of forward conduction or polarity and thus, application of a forward bias to the external ends of each wire results in that wire being made continuous whereas application of a reverse bias to the exterior ends of each wire results in that wire being rendered electrically discontinuous at the points where the diodes are located.
Depending upon the distance between diodes and the state of the wires, continuous or discontinuous, different phase shift values can be obtained for that part of an incident microwave which, on passing through the dielectric panels, encounters the wires.
By selectively controlling the state of the diodes in the various wires of dielectric panels making up a lens, the phase of the transmitted microwave can be made to vary, which results in a controlled deflection of the microwave beam passing through the lens.
The simplicity of such electronically controlled microwave lens, especially when used as an electronic scanner, represents a significant technological advance over conventional phase array systems. The simplicity of the panel lens is achieved since the wires mounted in the dielectric panels simultaneously fulfill two functions: the function of commanding the diodes and the function of acting as microwave components. Thus, the command of the diodes is not adversely affected by supplemental leads which constitute obstacles to microwave energy attempting to cross the dielectric panels of the lens. However, such panel lens have limited bandwidth and matching capabilities.
Furthermore, to achieve the simplicity of such electronic lens, all the diodes of each wire are required to be positioned in the same direction of forward conduction or polarity, so that forward and reverse biasing of each wire will result in a continuous wire, or discontinuous wire, respectively. However, it is desirable that a substantially higher voltage be employed to reverse bias the diodes than to forward bias the diodes. Thus, substantially greater voltage is required to render the wires discontinuous than to make them continuous. In fact, in large panel lens with high diode densities, for example, wherein two hundred or more diodes are employed in series for each wire, the required reverse bias for each wire becomes extremely high. In the above example, a reverse bias requirement of 50 volts for each diode results in an overall required reverse bias voltage of ten thousand volts.
These large voltages necessitate heavy insulation between different wires in the same panel and between wires of adjacent panels when a plurality of panels are employed one behind the other. Furthermore, these large voltages necessitate having heavy insulation between supply leads external to each panel and these large voltages create difficulties in building a system for applying large voltages to particular wires in small on/off switching times, for example, on the order of 10 microseconds, as is required in an electronically controlled dielectric panel lens.
Thus, the technique of biasing diodes by employing the same wire on which they are mounted as a biasing connection is useful when the number of diodes per wire is limited or when the reverse biasing voltage required to be applied to the diodes to render the wire discontinuous is small. However, such a technique is cumbersome when the number of diodes placed in series on a wire is large or when the required individual reverse bias voltage of each diode is large.
It is therefore an object of the present invention to increase the bandwidth of electronically controlled dielectric panel lens and to provide an electronically controlled panel lens of reduced biasing requirements.
Another object of the present invention is to provide a modification to the biasing arrangement of prior art electronically controlled panel lens permitting a reduction of the required reverse bias voltage while maintaining or improving the bandwidth of the panel lens and further while maintaining or improving the phase shift selectivity of the panel lens.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.